CURLDIGEST_BADALGO is a new return code from the digest code

typedef enum {

  CURLDIGEST_NONE, /* not a digest */

  CURLDIGEST_BAD,  /* a digest, but one we don't like */

  CURLDIGEST_BADALGO, /* unsupported algorithm requested */

  CURLDIGEST_FINE, /* a digest we act on */

  CURLDIGEST_LAST  /* last entry in this enum, don't use */